PT640019E - METHOD FOR THE TREATMENT OF SHEARS OF SHAVING SHEETS - Google Patents

Abstract

The present invention relates to an improved method of forming a polyfluorocarbon coating on a razor blade cutting edge comprising the steps of subjecting a fluorocarbon polymer having a molecular weight of at least about 1,000,000 to ionizing radiation to reduce the average molecular weight to from about 700 to about 700,000; dispersing the irradiated fluorocarbon polymer in an aqueous solution; coating said razor blade cutting edge with the dispersion; and heating the coating obtained to melt, partially melt or sinter the fluorocarbon polymer.

Description

64 ΟΟΊ ^

DESCRIPTION

METHOD OF TREATMENT OF SHEAR BLADES

This invention relates to an improved method for producing cutting edges of razor blades by coating the blade edge with an aqueous dispersion of polyfluorocarbon and subsequent heating of the polyfluorocarbon. The present method provides good telomer adhesion and good blade performance, further eliminating the need to use environmentally harmful solvents.

Uncoated razor blades, although sharpened, can not be employed to dry beard without excessive discomfort and pain, and it is necessary, for a practical matter, to employ with these slides a beard softening agent such as water and / or a shaving cream or soap. The pain and irritation produced by the shaving action with uncoated blades is due to the excessive force that is required to draw the cutting edge of the blade through the unshaven hairs of the beard whose force is transmitted to the nerves in the skin adjacent to the hair follicles a from which the beard hairs extend, and, as is well known, the irritation produced by the excessive pressure exerted on these hairs may continue for a considerable period of time after the shaving action has ceased. Blade coatings have been developed to solve these problems. U.S. Patent 2,937,976 issued May 24, 1960 to Granaham et al. Discloses a "coated" blade that provides a reduction in the force required to cut the beard hair. The coating material consists of a polymer containing organic silicon which is partially chemically treated as a gel which remains adherent to the sheet. Although these coated blades have known considerable commercial success, the coatings were not permanent and were spent relatively quickly. U.S. Patent 3,071,856 issued January 8, 1963 to Fischbein discloses the fluorocarbon coated blades, and in particular the polytetrafluoroethylene coated blades. The blades may be coated by (1) positioning the blade edge near a fluorocarbon source and subsequently heating the blade, (2) spraying the blade with a fluorocarbon dispersion, (3) rapidly immersing the blade in the fluorocarbon dispersion or (4) by use of electrophoresis. Example 2 shows a slide that is dip coated in an aqueous colloidal dispersion containing 25% (by weight) finely divided solid tetrafluoroethylene polymer (Teflon Clear Finish from DuPont). The resulting slide was then subjected to agglomeration treatment. U.S. Patent 3,118,110, issued June 30, 1970 to Fischbein, discloses an improved solid fluorocarbon telomer for use in the coating of safety razor blades. The solid fluorocarbon polymer has a melting point between 310Â ° C and 332Â ° C and has a melt flow of between 0.005 and 600 grams per ten minutes at 350Â ° C. The molecular weight is estimated to be between 25,000 and 500,000. For best results, the solid fluorocarbon polymer is divided into particles of between 0.1 and 1 μm. Example 2 describes an aqueous dispersion of 0.5% polytetrafluoroethylene, PTFE (Impurities: 0.44% Chlorine and 0.06% Hydrogen), and 0.5% Triton X-100 surfactant. The dispersion is electrostatically vaporized over the stainless steel blades. Example 8 reports that the polymerization of tetrafluoroethylene is achieved in an aqueous dispersion with methyl alcohol acting as chain transfer agent and with ammonium persulfate acting as a catalyst. U.S. Patent 3,658,742 issued April 25, 1972 to Fish et al. Discloses an aqueous polytetrafluoroethylene (PTFE) dispersion containing Triton X-100 surfactant which is electrostatically vaporized over the edges of the blades. The aqueous dispersion is prepared by replacing the Freon solvent in the Vydax brand PTFE dispersion (PTFE + Freon solvent), distributed by E. I. Dupont, Wilmington, Delaware, by the isopropyl alcohol and then exchanging the isopropyl alcohol with water. Example 1 describes an aqueous PTFE dispersion containing 0.4% PTFE and 0.1% Triton X-100 surfactant. U.S. Patent 3,766,031, issued Oct. 16, 1973, to Dillon, indicates that the application of a critical dose of ionizing radiation to agglomerated or unglomerated polytetrafluoroethylene renders this material capable of being microscopically divided without any heat side effect, and the resulting particles are readily dispersible in various media. Such particles have the extremely low coefficient of friction 2 associated with the polytetrafluoroethylene resin. The ionizing radiation dosage level according to the process of the present invention is in the range of about 5 megarads to about 25 megaads, and is preferably maintained between about 10 megarads and 25 megarads. European Patent Application 0 017 349, filed March 6, 1980, discloses that the agglomerated polytetrafluoroethylene can be degraded non-destructively until reduced to a powder having an average particle size of less than 10 μΐη by a combination of electrons or other sub-atomic particles in the presence of oxygen or air and simultaneous or subsequent heating at temperatures below the melting point of the material. The preferred irradiation range, temperature and heating time in terms of efficiency and economy are about 50-150 mads, between 65 ° C and 315 ° C (150 ° F to 600 ° F) for at least about half an hour depending on the desired average particle size characteristics and the melt rate and acceptable particle yield characteristics.

Previous attempts to apply aqueous polyfluorocarbon dispersions in sheet coating processes have produced unacceptable adhesion or required an unacceptably high force to cut the hairs. In addition, the polyfluorocarbon coating was worn too quickly as evidenced by a significant increase in the force required to cut or separate the beard hair after successive uses.

It is an aim of the present invention to provide a non-harmful method for the environment of edging razor blades with polyfluorocarbons, and in particular with polytetrafluoroethylene. Specifically, it is an object of the present invention to eliminate the chlorofluorocarbon solvents and the volatile organic solvents from the sheet coating process. It is also an object of the present invention to provide a razor blade cutting edge which produces cutting and use characteristics substantially the same as those coated with chlorofluorocarbon dispersions.

These and other objects will be apparent to one skilled in the art from the following: The present invention relates to an improved method of forming a polyfluorocarbon coating on the cutting edge of a razor blade comprising the steps of subjecting the fluorocarbon in the form of a powder having a molecular weight of at least about 1,000,000 ionizing radiation to reduce its average molecular weight to between about 700 and about 700,000; dispersing the irradiated fluorocarbon polymer in an aqueous solution; coating said cutting edge of the razor blade with the dispersion; and heating the coating obtained to melt, partially melt or agglomerate the fluorocarbon polymer.

According to the present invention there is provided a method of forming a polyfluorocarbon coating on the cutting edge of a razor blade comprising the steps of: (a) subjecting the fluorocarbon polymer powder having an average molecular weight of at least 1,000. 000 g / mol at a dose of ionizing radiation of between 20 and 80 megarad to reduce its average molecular weight to between 700 and 700,000; (b) dispersing the irradiated fluorocarbon polymer into an aqueous solution which is free of chlorofluorocarbon solvents; (c) coating said cutting blade with the dispersion; and (d) sufficient heating of the coating to adhere the fluorocarbon polymer irradiated to the edge of the blade.

All percentages and ratios given herein refer to a mass basis unless expressly stated to the contrary.

As used herein the term "cutting edge of a razor blade" includes the cut point and facets of the blade. Applicant recognizes that the blade may be coated in its entirety as described herein; however, it is not believed that such a wrapping coating is essential in the context of the present invention. 4

Additionally, terms like " ionizing radiation " or " irradiated ", as used herein, refer to the emission of X-rays, β-rays, gamma rays, electrons or positrons. Gamma radiation is preferable. Various methods have been proposed in the past for the preparation and use of aqueous dispersions of fluorocarbon polymers in the razor blade edged coating. All these methods invariably produced a blade whose cutting efficiency rapidly diminished. Surprisingly, the inventor has found that when the irradiated fluorocarbon polymer, and in particular the irradiated polytetrafluoroethylene polymer, is used, the sheets exhibit a significant improvement in their long-term efficacy compared to the results provided by the aqueous systems of the prior art. The blades produced by the present invention require the application of a much smaller force to cut the hair softened by water. This reduction in shear force persists for several successive uses with the same cutting edge of the blade.

According to the present invention, an aqueous dispersion is prepared from an irradiated fluorocarbon polymer. Preferred non-irradiated fluorocarbon polymers (ie, the starting material) are those containing a chain of carbon atoms including a preponderance of -CF2-CF2- groups, such as tetrafluoroethylene polymers, including copolymers such as those with a minor proportion, for example up to about 5% by weight, of hexafluoropropylene. These polymers have terminal groups at the ends of the carbon chains which may vary in nature, depending, as is well known, on the method of preparing the polymer. Among the common terminal groups of such polymers are 0 -H, -COOH, -Cl, -CCI3, -CFICF2 C1, -CH2 OH, -CH3 and the like. Although the molecular weights and the precise molecular weight distribution of the preferred polymers are not known with accuracy, they are believed to have molecular weights above 1,000,000. Among the chlorine-containing polymers, those containing from 0.15 to 0.45% by weight chlorine (which is present in the terminal groups) are preferred. Blends of two or more fluorocarbon polymers may be used, provided the blends have melt and melt rate characteristics as specified above, even though the individual polymers forming the blend do not have these characteristics. The most preferred starting material is polytetrafluoroethylene. 5

According to the present invention, there is provided a method of forming a razor blade cutting edge polyfluorocarbon coating, which comprises subjecting the aforementioned starting material, i.e. the fluorocarbon polymer, to a molecular weight of at least 1,000,000 in the form of a dry powder, the ionizing radiation to reduce the average molecular weight of the polymer to between about 700 and about 700,000, preferably between about 700 and about 51,000, and more preferably for about 25,000, forming a dispersion of the irradiated polymer in an aqueous medium; spraying the dispersion over the cutting edge of the razor blade and heating the coating obtained to adhere the polymer to the blade edge. The heating of the coating is intended to adhere the polymer to the blade. The heating operation may result in agglomerated, partially molten or molten coating. A partially cast or fully melted coating is preferable because it allows the coating to spread and cover the blade more fully. For a more detailed discussion of fusion, partial melting, or agglomeration, see the McGraw-Hill Encyclopedia of Science and Technology. Vol. 12, 5th edition, p. 437 (1902). The radiation dose is preferably between 20 and 80 megarads and the ionizing radiation is preferably comprised of gamma rays from a Co60 source. The polyfluorocarbon is preferably polytetrafluoroethylene and the irradiation is preferably performed to obtain a telomer having an average molecular weight of about 25,000.

For the purpose of forming the dispersion which is vaporized on the cutting edges, the irradiated polyfluorocarbon should be in the form of finely divided particles, preferably with an average particle size of no more than about 100 μl. The polyfluorocarbon starting material in powder form is usually available as a material having a particle diameter greater than this value and which can be brought to this particle diameter either before or after the irradiation step, with preference given to this second hypothesis. Typically, the level of the polyfluorocarbon in the dispersion is between 0.5% and 2.0% (by weight), preferably between 0.7% and 1.0% (by weight). 6

In a preferred embodiment, the particle size range is between about 2 μm and about δ μην For these particles a surfactant is required. Generally, the surfactants for use in the present invention may be selected from the various materials that act on the surface tension of liquids and which are available for use in aqueous polymer dispersions. Such surfactants include the alkali metal salts of dialkyl sulfosuccinates, high molecular weight fatty acid soaps, fatty amines, sorbitol mono and diesters of fatty acids and their polyoxyalkylene ether derivatives, alkali metal salts of alkylaryl sulphonates, glycols of polyalkylene ether and the mono and diesters of fatty acids of said glycols. Preferred surfactants in the context of the present invention are nonionic alcohols and more particularly alcohols of alkylphenylpolyalkylene ethers such as Triton X-100 and Triton X-114 marketed by Union Carbide, Ipegal CO-610 available from Rhone-Poulenc and Tergitol 12P12 marketed by the Union Carbide Company. Especially useful results were obtained using Tergitol 12P12 which is the dodecylphenyl polyethylene ether alcohol containing 12 ethylene oxide groups. Generally, the amount of surfactant employed may vary. Usually, the surfactant is used in amounts equal to at least 1% by weight of the fluorocarbon polymer, preferably at least about 3% by weight of the fluorocarbon polymer. In preferred embodiments, the surfactant is used in amounts ranging from 3% to 50% by weight of the polymer with lower levels of surfactant being desired. Particularly good results were obtained using from 3% to 6% of surfactant.

Nonionic surfactants are often characterized in terms of their HLB (Hydrophile-Lipophilic Equilibrium) number. For single alcohol ethoxylates, the HLB number can be calculated from the formula: wherein E is the weight percent of ethylene oxide in the molecule.

Essentially, any surfactant having a Hydrophile-Lipophile Equilibrium number between 12.4 and 18, and preferably between 13.5 and 18.0, may be used in the present invention. For a more in-depth discussion of the HLB numbers see Kirk-Othmer, Encyclopedia of Chemical Technoloav. Vol. 22, p. 360-362. 7

This dispersion may be applied to the cutting edge in any suitable way to generate a coating as uniform as possible, such as for example by rapid immersion or by spraying; the nebulization being especially preferred for coating the cutting edges, in which case an electrostatic field is preferably employed in conjunction with the nebulizer in order to increase the deposition efficiency. For further discussion of this electrostatic spraying technique see U.S. Patent 3,713,873 issued to Fish on January 30, 1973. Preheating the dispersion may be desirable to facilitate spraying, the extent of preheating being dependent of the nature of the dispersion. Preheating the slides to a temperature near the boiling point of the volatile liquid may also be desirable.

In either event the blades containing the polymer particles deposited on their edges must be heated to an elevated temperature to form a coating adhering to the cutting edge. The time period during which the heating is continued may vary widely, from as little as a few seconds to as many as a few hours, depending on the identity of the particular polymer used, the nature of the cutting edge, the speed at which the blade is brought to at the desired temperature, the temperature reached, and the nature of the atmosphere in which the blade is heated. While the blades may be heated in an atmosphere of air, it is preferred that they are heated in an inert gas atmosphere such as helium or nitrogen, or in an atmosphere of reducing gas such as hydrogen, or in mixtures of such gases, or in vacuum . The heating must be sufficient to allow the individual particles of the polymer to at least agglomerate. Preferably, the heating should be sufficient to allow the polymer to spread on a substantially continuous film of the appropriate thickness and to make it firmly adherent to the blade edge material.

The heating conditions, i.e. the maximum temperature, the time interval, etc. will obviously have to be adjusted in order to avoid significant polymer decomposition and / or excessive tempering of the cutting edge metal. Preferably, the temperature should not exceed 430 ° C.

The following specific examples illustrate the nature of the present invention. The quality of the first beard made with blades of each of the following examples is equal to the quality obtained with the fluorocarbon coated blades manufactured with the currently available chlorofluorocarbon solvent, and the decrease in quality over successive shavings in the case of blades of each particular type is less than the decrease in quality in the case of fluorocarbon coated blades made from the previously known aqueous solvent. EXAMPLE 1 Polytetrafluoroethylene powder having an average molecular weight of about 3 million is subjected to gamma irradiation so that the dosage received is 25 megarad and that the average molecular weight value is 25,000 as calculated by the method described by Sewa et al J. App. Polymer Science, 17, 3258 (1973). EXAMPLE 2

A dispersion containing 1% by weight of the irradiated material of Example 1 reduced to a particle size of between about 2 μm and about 8 μm and 0.03% Triton X-100 (Union Carbide) surfactant in water at 50 ° C is prepared and homogenized with a blender. Cutting edges of stainless steel razor blades are then electrostatically sprayed with the dispersion. After drying, the blade edging is heated under nitrogen at 650 ° F (343 ° C) for 35 minutes. Slides treated in this way exhibit an equivalent shear performance and the same durability of the coating as similar slides which had been treated in the same manner with the commercially available solventless trichlorotrifluoroethane unmanned telomer. EXAMPLE 3

A dispersion containing 0.7% by weight of the irradiated material of Example 1, water at 50 ° C and 0.05% surfactant Brij 58 (ICI Americas) is prepared and homogenized with a blender. Cutting edges of stainless steel razor blades are then electrostatically sprayed with the dispersion. After drying, the blade-face coating is agglomerated in nitrogen at 650 ° F (343 ° C) for 35 minutes. Slides treated in this way exhibit an equivalent cutting performance and the same durability of the coating as similar slides which had been treated in the same manner with the commercial unavailable non-irradiated telomer in isopropanol or trichlorotrifluoroethane.

Lisbon, 1 MAR. 2000 By THE GILLETTE COMPANY

Official Agent of the Industrial Property Arc © da Conceição, 3,1 »- 1100 LISBON 10

Claims (9)

A method of forming a polyfluorocarbon coating on the cutting edge of a razor blade comprising the steps of: (a) subjecting the fluorocarbon polymer powder having an average molecular weight of at least 1,000,000 g / mol to one dose ionizing radiation of between 20 and 80 megarad to reduce its average molecular weight to between 700 and 700,000; (b) dispersing the irradiated fluorocarbon polymer into an aqueous solution which is free of chlorofluorocarbon solvents; (c) coating said cutting blade with the dispersion; and (d) sufficient heating of the coating to adhere the fluorocarbon polymer irradiated to the edge of the blade. A method according to claim 1, wherein the heating of step (d) is sufficient to melt, partially melt or agglomerate the polymer, preferably to partially melt or melt the polymer. A method according to claim 1 or 2, wherein the fluorocarbon polymer of step (a) is reduced to an average molecular weight of between 700 and 51,000 g / mol, more preferably to about 25,000 g / mol, by ionizing radiation. A method according to any one of the preceding claims wherein the fluorocarbon is irradiated as a dry powder, and preferably the irradiated fluorocarbon of step (b) has an average particle size of not more than 100 μιτι. A method according to any one of the preceding claims, wherein the level of irradiated fluorocarbon dispersed in the aqueous solution of step (b) is (1) between 0.5 and 2.0% by weight, or (2) between 0 , 7 and 1.0% by weight. A method according to any one of the preceding claims, wherein the fluorocarbon polymer is polytetrafluoroethylene. 1 A method according to any one of the preceding claims, wherein the aqueous solution of step (b) comprises one of the following characteristics: (1) further comprising a surfactant; (2) further comprises a surfactant having an HLB (Hydrophile-Lipophilic Equilibrium) number between 12.4 and 18; (3) further comprises a surfactant having an HLB (Hydrophile-Lipophilic Equilibrium) number between 13.5 and 18; or (4) further comprises a surfactant in an amount of at least 5% by weight of the irradiated fluorocarbon polymer, said surfactant consisting of one or more alkali metal salts of dialkyl sulfosuccinates, high molecular weight fatty acid soaps, fatty amines and sorbitol diesters and their polyoxyalkylene ether derivatives, alkali metal salts of alkylaryl sulphonates, polyalkylene ethers of glycols or fatty acid mono- and diesters of said glycols. A method according to claim 7, wherein the razor blade shear coating is produced by an electrostatic spray technique. A method according to claim 7 or 8, wherein the irradiated fluorocarbon of step (b) has a particle size of between 2 and 8 μηη. Lisbon, 1 MAR. 2000 By THE GILLETTE COMPANY Official Agent of the Industrial Property Arco da Conceição, 3.1? The present invention relates to an improved method for forming a polyfluorocarbon coating on the cutting edge of a razor blade comprising the steps of subjecting a fluorocarbon polymer with a molecular weight of at least about 1,000,000 ionizing radiation to reduce its average molecular weight to between about 700 and about 700,000; dispersing the irradiated fluorocarbon polymer in an aqueous solution; coating said cutting edge of the razor blade with the dispersion; and heating the coating obtained to melt, partially melt or agglomerate the fluorocarbon polymer.